At Lakeville South High School, 60% of students have high-speed internet access, 30% have a mobile computing device, and 20% have both. The proportion of students that have neither high-speed internet access nor a mobile computing device is:
A. 0%
B. 10%
C. 30%
D. 80%
E. 90%
Note: the answer is 30% but I can't for the life of me figure out why
